The invention relates to an anchor element for knotless fixing of tissue to a bone by means of at least one suture threaded through the anchor element.
Generally, such anchor elements, also called suture anchors, are used in the medical field to ensure that tissues, mostly tendons, that have become detached from a bone can be fixed back onto the bone.
For this purpose, the anchor element and a suture connected to the anchor element are driven firmly into the bone. The protruding suture ends are connected to the detached tissue, by which means the detached tissue is fixed to the bone.
In a first operating technique, known in particular from U.S. Pat. No. 5,690,676, the anchor element is designed such that it has an approximately cylindrical body on whose outer face there are projections that prevent removal of the anchor element after it has been inserted into the bone. These projections can be designed as barb-like elements, for example if the anchor element is driven into the bone, or they can also be designed as an outer thread if the anchor element is turned into the bone in the manner of a screw. The suture is threaded through the transverse bore extending through the body, and the two suture ends are placed in outer longitudinal grooves on the body and guided in the proximal direction. A device called a driver is engaged on the proximal end of the anchor element, and it is usually mounted onto the proximal end of the anchor element. The two suture ends are guided along the driver device and are wound there onto radially projecting stubs for the driving-in procedure.
After the anchor element has been driven into the bone and the driver device has been removed, the two free suture ends are used to secure the detached tissue. To do so, the two suture ends are knotted onto the detached tissue, for example a tendon, lying closely on the bone.
The anchor element anchored in the bone, and the bone itself, form the force/abutment points between which the tissue is fixed.
A disadvantage of this operating technique is that the knotting requires considerable experience and dexterity on the part of the operating surgeon. Such knots can come undone, or soft-tissue bridges can form around the knot because the knot is arranged on the outside of the operating site.
In a development of this operating technique, so-called knotless anchors were developed, which are known for example from US 2004/0138706 A1 and which form the subject matter of the present invention.
This anchor element has a body on whose outer face there are projections that prevent removal of the anchor element inserted in the bone. A transverse bore is arranged in the distal end area of the body and extends through the latter. A suture is threaded transversely through the body. A clamp element is provided which is moveable along the body and is used to clamp the suture. The clamp element is designed as an outer axially moveable sleeve.
In this operating technique too, the suture is first threaded through the anchor element. One of the free suture ends is pushed, mostly with the aid of a needle, through the tissue to be fixed, and the pushed-through end is then threaded back in the opposite direction through the transverse bore in the anchor element. The connection between the anchor element and the tissue to be fixed takes the form of a suture loop. The anchor element can now be introduced into the bone, together with the suture after which the free suture ends are pulled so that the protruding loop of the suture, connected to the tissue, is drawn toward the fixing location.
The relative position between the suture and tissue connected to it, and the anchor element is now fixed not by forming a knot, but instead by moving a clamp element through which the suture is fixed or as it were clamped in a defined position on the anchor element. In this way, the loop holding the tissue is also fixed. The protruding free ends can then be cut off, for example, and there is no need to apply a knot.
In the US 2004/0138706 A1, the clamp element is designed as a sleeve which is mounted on the outside of the body of the anchor element. The sleeve and body are displaceable relative to one another.
In one position of displacement of the sleeve, the suture threaded through the body is freely movable, for example so that the tissue pierced by the suture can be drawn onto the bone and fixed in its position. The sleeve is then moved in order to clamp the suture and fix it in its relative position.
As can be seen in particular from moving from FIG. 4 to FIG. 5 of US 2004/0138706 A1, there are several relatively sharp-edged clamp points between which the suture is squeezed. This results in relatively high shearing forces, which means that damage to the suture, and therefore tearing-off of the suture, cannot reliably be ruled out.
In addition, the outer sleeve is a very complicated structural part which, in order to exert a clamping force, has to be slightly spread open by the anchor element. For this purpose, suitable lock-type bridges are needed between the outer face of the body of the anchor element and the inner face of the sleeve, which make release from this locked position difficult or impossible. For this reason, corrective measures, for example during temporary release of the clamping connection, can only be carried out with difficulty, if at all.
It should be borne in mind that the dimensions of such clamp elements involve lengths in the range of several centimeters and diameters of several millimeters.
Therefore, not only is the production of such parts extremely complex, their handling is also very difficult and, in particular, their stability in respect of the holding or fixing force is extremely problematic.
If a tendon subjected to high loading, for example a tendon from the shoulder area or the knee area, is fixed, it is evident that considerable tensile forces from the tendon act on the assembled structure introduced into the bone and composed of body, clamp element and clamped suture.
If one considers the aforementioned dimensions, it will be evident that the wall thickness of the outer sleeve may at best be in the range of fractions of millimeters, although it is this structural part that is intended to provide the clamping force for holding the suture.
Since the sleeve, because of its construction, covers a certain proportion of the outer face of the body of the anchor element, but this anchor element serves to hold the whole assembly in the bone via the projections present on its outer face, suitable structural measures have to be taken to ensure that the body of the anchor element as such can in fact be safely anchored in the bone.
This leads to additional and considerable outlay in terms of construction.
It is an object of the present invention to provide an anchor element for knotless fixing a tissue, which is of simple construction, ensures effective anchoring of the anchor element and, at the same time, allows the suture to be fixed efficiently and without damaging it.